The invention refers to a method for pulling a semiconductor single crystal according to the Czochralski method, in which a semiconductor melt is produced in a quartz glass crucible and the semiconductor single crystal is pulled therefrom, the quartz glass crucible comprising an inner wall and the semiconductor melt comprising a free melt surface which in the area of a contact zone extending radially circumferentially on the inner wall of the crucible are in contact with each other and with a melt atmosphere, respectively, wherein primary vibrations of the melt that start from the contact zone are initiated.
Furthermore, the invention refers to a quartz glass crucible to be used for pulling a semiconductor single crystal according to the Czochralski method.
In the so-called Czochralski method, semiconductor material, such as silicon, is molten in a quartz glass crucible and a seed crystal of a silicon single crystal is supplied from above to the melt surface, resulting in the formation of a melt meniscus between crystal and melt. The single crystal is slowly drawn off upwards under rotation of the crucible and/or the single crystal, the semiconductor single crystal growing on the seed crystal. This process shall be called “starting process” or shortly “starting” in the following. Interactions between liquid and solid phase take place on the solidification front between single crystal and semiconductor melt; these are impaired by convection or oscillation of the melt. These movements of the melt can be caused or intensified by temperature or substance gradients within the liquid, by rotation of melt and seed crystal or by immersion of the seed crystal. Particularly disadvantageous are oscillations of the melt. It is known that these occur whenever the chemical potential between the three phases semiconductor melt, melt atmosphere and crucible changes periodically.
Such oscillations impair not only the quality of the semiconductor single crystal. They are particularly disadvantageously noticed in the starting process as they aggravate nucleation and can delay or even impede the same by one to several days. This reduces productivity and can go so far that the life of the quartz glass crucible is already exceeded in the starting process, or that dislocations are produced in the single crystal that require a re-melting of the solidified silicon.
The quartz glass crucibles used in the Czochralski method are normally provided with a transparent inner layer on an opaque outer layer which contains pores. In the crystal pulling process the transparent inner layer is in contact with the silicon melt and is subject to high mechanical, chemical and thermal stresses. To reduce the corrosive attack of the silicon melt and, together with this, the release of impurities from the crucible wall, the inner layer is as pure as possible and homogeneous and has hardly any bubbles.
The inner layer of synthetically produced quartz glass ensures a low concentration of impurities in the region near the melt and has in this respect an advantageous effect on the yield of pure and dislocation-free semiconductor single crystal. However, it has been found that crucibles with an inner layer of synthetic quartz glass as compared with quartz glass crucibles produced from naturally occurring quartz sand rather tend to cause oscillations of the melt surface.